A fantastic article about using Cisco CBAC to filter network traffic and prevent DoS

A Denial-of-Service (DOS) attack can cause immense harm to your business. In this chapter, you can learn how to deal with such an attack, and minimize the damage done.

Of the three categories of attacks—reconnaissance, access, and denial-of-service (DoS)—DoS attacks are the easiest to implement yet the hardest to defeat. DoS attacks are based on packet flooding, which uses up bandwidth, CPU, and memory resources on not just the victim device, but also intervening devices, such as routers, switches, and firewalls.

When you are experiencing a DoS attack, one of the first things you need to do is find out the actual kind of DoS attack that is affecting your network. As you will see in the first section of this chapter, a variety of options are available to you, including examining the CPU utilization of your routers, using ACL statements with logging parameters, and using NetFlow.

When you know the kind of DoS attack directed at your network, you can implement an appropriate solution. The remaining sections in this chapter focus on these solutions, including TCP Intercept, CBAC, and rate limiting. Of course, you always can use an ACL to block offending traffic; however, this might introduce other problems, such as the blocking of legitimate traffic. Therefore, in many cases, you need to use other tools, such as the ones discussed in the last half of this chapter, to deal with DoS issues.

Cisco Router Firewall Security: DoS Protection Chapter

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